The long-term goal of the proposed research is to gain further understanding of the neural mechanisms involved in the production of coordinated behaviors. Specifically, this study will focus on the leg motor patterns produced by chicks as part of their normal behavioral repertoire and relate these to central pattern generating circuitry (CPG) output. The chick is an ideal subject because it is accessible throughout its entire life cycle, during which it produces a wide variety of different behaviors that involve distinctive leg motor patterns. These studies will use quantitative analysis of kinematic (joint angle), electromyographic (EMG) and electroneurographic (ENG) data. First, the range of leg motor output patterns (including movements and underlying muscle contraction patterns) seen in 15 different behaviors in embryonic and posthatching chicks will be characterized (Aim 1). Further analysis of these data will be used to determine the relationship among these leg motor patterns by looking for constraints, which may indicate similarities in uderlying mechansims, and quantifying the differences, which may suggest which features are most susceptible to modulation (Aim 2). Next, the responses obtained when 2 different motor patterns are elicited simultaneously will be analyzed. These data on interactions between motor patterns will be used to examine the issue of whether the pattern generating circuitry for the different behaviors is overlapping or separate (Aim 3). After, characterizing the leg motor patterns and their inteactions in intact animals, the output of the isolated spinal cord will be analyzed. These data will provide information on the relationship between the CPG output pattern(s) and the motor patterns involved in producing specific behaviors in intact chicks (Aim 4). Finally, the role of specific sources of sensory input will be evaluated to determine how they are used to modulate CPG circuitry to produce the leg motor patterns underlying specific behaviors (Aim 5). Overall, the data generated in achieving these 5 Aims will significantly increase our understanding of how coordinated motor behaviors are produced. The mechanisms used in chicks are likely to be general ones, found throughout the vertebrates, including humans.